The present invention relates to an impression appliance for dental purposes, in which a reception channel for dental impression materials is adapted to the shape of the human jaw and is horseshoe-shaped. This channel is bounded on one side by a base plate and along its inner and outer edge by sections turning upward from the base plate plane in the same direction. These sections are provided on the channel inside with retention edges that are away from the base plate and have undercuts in the area of the open channel side; the invention also relates to a method for manufacturing such impression appliances, and to a tool for implementing this method.
Impression appliances are used for making impressions of teeth and gums. The impression is a negative reproduction of the teeth or gums. It is made by filling the reception channel of an impression appliance with plastic hardening material, placing the appliance in the patient's mouth and pressing it against the upper or lower jaw of the patient so that the teeth or gums are fully reproduced in the plastic material as a negative. After the dental impression material has hardened, the impression appliance with the material in its reception channel is withdrawn from the teeth or the gums, retaining the negative reproduction of the teeth or gums.
By pouring plaster of Paris into these impressions, true models of the teeth and gums are obtained. Such models are used in dentistry for diagnostic, jaw-orthopedic and prothesis purposes.
Impression appliances should ensure that, on the one hand, the plastic impression material during contact with the teeth or gums forms an exact reproduction of the latter, and, on the other hand, that this reproduction is preserved when the appliance is removed from the mouth of a patient, i.e., that the reproduction does not become deformed or detaches from the appliance. This requiremnet is satisfied only inadequately by the appliances known up to now.
To improve the adherence of the impression material to the appliance, it has been proposed that the walls of the reception cavity or channel for the impression material be provided with perforations. This measure ensures that, during removal of the impression from the patient's mouth, damage to the impression is avoided. However, it has been found difficult to obtain good impressions with such perforated walls in the area of the reception channel for the impression material, because upon applying impression material, the contact pressure is reduced by the perforations in the appliance.
Impression appliances whose reception cavities for the impression material are confined by closed walls do not have this drawback. However, with such appliances, while removing an impression from a patient's mouth, the impression easily detaches, and undesirable and frequently unnoticed changes of the impressions occur.
Since even non-perforated impression appliances have been found unsatisfactory, it has also been suggested that along the inside edges of the reception cavities, which mostly form U-shaped channels, there be soldered to the appliance partitions, so-called retention edges in the form of peripheral wires. Such impression appliances will meet practical requirements as long as the soldered retention edges are intact. However, it has been found that the soldered retention edges easily detach, especially when removing a hardened impression from such an appliance. As a result, these rather expensive appliances frequently become useless after a brief period of use.
In view of the inadequacies prevailing in the state of the art, it is the object of the present invention to provide an impression appliance as initially described, which equally ensures an exact reproduction of the teeth or gums, and the preservation of this reproduction during removal of such impression from a patient's mouth. In addition, the impression appliance to be provided is to have much durability, and must be economical to produce.
Accordingly, another object of the present invention is to provide a process for manufacturing such impression appliances and a tool suitable for implementing the process.